Cyclodialysis is the result of the separation of the longitudinal fibres of the ciliary muscle from their scleral insertion, creating states of ocular hypotony. It is mainly caused by traumatisms. Gonioscopy has traditionally been the diagnostic test for this entity, however, at present it is being replaced by other techniques, such as ultrasound biomicroscopy (UBM). We present the case of a 57-year-old male who, following a traumatism in the left eye caused by the disc of a radial saw, presented corneal perforation and vitreous haemorrhage with pan-retinal edema. The gonioscopy was normal in spite of the existence of persistent ocular hypotony. The realization of a UBM enabled diagnosis of a small cyclodialysis of less than ten degrees. Surgical treatment made it possible to recover normal intraocular pressure.